Uncovering the cation effects on the electroreduction of CO2 on Pd/C catalysts − an SEIRAS study

Electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) has long been known to be affected by the electrolyte cations, yet the interpretations of these effects remain controversial. In this work, taking advantage of the unique catalytic characteristics of Pd, we investigated the cation effects on the CO2RR. It was found that the productions of formate and carbon monoxide (CO) are accelerated, and the competitive hydrogen evolution reaction (HER) is suppressed on Pd surfaces by larger cations. Detailed ATR-SEIRAS measurements revealed the promotion of CO2RR comes from two aspects. First, the CO2 molecules can be concentrated at the electrode–electrolyte interface by larger cations through electrostatic interaction. Second, a stronger interfacial electric field brought by the larger cations can accelerate the CO2RR and stabilize the negatively charged intermediates. The potential-dependent spectral transitions of adsorbed CO and interfacial water shed new light on the cation-dependent electric double layer structures. In light of these findings, the cation effects on the formate and CO pathways at different overpotentials were further revealed.